A pressure sensor of this type is used to detect the air pressure in the interior of so-called tubeless tires in motor vehicles. The air pressure in such tires is highly important for both vehicle road holding quality and tire life. In the context of the measurement of important vehicle data, it would appear desirable for this tire pressure also to be detected and monitored as accurately as possible.
The problem in obtaining these measured values is that during vehicle operation, as when the tires are mounted or removed, tires undergo considerable mechanical strain, which can cause sensor damage, particularly with sensitive sensors, which are inherently desirable. There is also the problem that the centrifugal forces involved can falsify the measurements made by the pressure sensors.
From U.S. Pat. No. 4,237,728, an apparatus is known which enables an indirect, rough ascertainment of the tire pressure by means of an elastically deformable feeler protruding radially outward from the drum-like central rim portion; the feeler is deflected whenever the tire cross section varies, for instance, when because of a pressure drop, the inside wall of the tire comes to rest on the feeler. The feeler is connected to a piezoelectric crystal, and the resultant compression of the piezoelectric crystal generates a voltage, from which the measurement signal is derived. This previously known measuring system is accordingly relatively insensitive and is substantially suitable only for detecting highly abnormal conditions. Because of the insensitivity of the feeler provided in the prior art, falsification of the measured results is less serious.